Hurk-

You've encountered the "Chinese Standard" screw... a 6-32 winds up being 5.75-31, and a 10-24 is actually 9.87-21. [Linked Image]

And no, they're not metric. I've got a full kit of M standard and they didn't fit right either.

Of course, the makers of the screwdriver style tap tools are probably giddy over this influx... I know it's why I bought my Klein 6-in-1.